Effects of extreme precipitation on sediment connectivity in a farmland watershed of the gully region, the Loess Plateau of China

Connectivity has emerged as a useful concept for exploring the movement of water and sediments between landscape locations and across spatial scales. Studies on the influences of extreme precipitation events on sediment connectivity of slope-gully systems in a small watershed can provide a theoretical basis for comprehensive watershed management. Taking the farmland watershed in Caijiachuan watershed in Ji County of the Loess plateau as the research area, UAV and remote sensing images were used to carry out field investigations on a slope and gully system before and after the extreme precipitation event occurred in October 2021. The landscape patterns before and after extreme rainstorm were analyzed, the sediment connectivity of the slope-gully system was quantified, and the spatial distribution and topographic features of landslide points were identified, the responses of typical engineering measures to extreme precipitation was evaluated. The results showed that: (1) the rainfall event lasts 84 hours, with a cumulative rainfall of 160.4 mm, a rainfall intensity of 1.9 mm/h and a rainfall frequency of 0.16%. It was an extreme rainstorm that comes once in a hundred years. (2) After the rainstorm, the number of patches increased, the landscape shape index increased, the Contag index decreased, and the Shannon diversity index decreased. (3) Sediment connectivity was unevenly distributed in the watershed before the rainstorm, but it increased after the rainstorm. (4) After the rainstorm, the sediment connectivity of the landslide site decreased, and the landslide mainly occurred at 0-10°and 40-50°, accounting for 29.11% and 17.74%, respectively. After the occurrence of extreme rainfall, landscape pattern fragmentation and richness of the slope-gully system decreased. Landslides induced by extreme rainfall events affect sediment connectivity, and the sediment connectivity index could be used to identify landslide sites and assess the response of typical soil and water conservation engineering measures to extreme rainfall. The results of the study could provide support for integrated watershed management and ecological restoration after extreme precipitation events.

Keywords: Extreme precipitation; Check dam; Sediment connectivity; Integrated watershed management